Photoluminescence in single-layer MoS2: The role of impurities and doping

Photoluminescence is an important property intervening in the efficiency and performance of single-layer MoS2 optoelectronic devices. The variation of photoluminescence with impurities related to the environment and the substrate and dependence on temperature, illumination, and doping can give information on the mechanisms involving trapped, bound, and free charges. In this work, we measure photoluminescence in exfoliated single-layer MoS2 on a variety of substrates and environments, as a function of temperature, gating, and laser power concluding that extrinsic impurities and defects are dominant as dopants and as trapping centers. Adsorbates from the environment act as electron acceptors and tend to reduce the intrinsically n-doped character of MoS2. On the other hand, an interaction between impurities on substrates, such as glass or silicon dioxide, leads to an increase in n-doping of MoS2 and creation of positively charged traps for excitons and free charge. We identify the doping and charge trapping mechanisms influencing photoluminescence and account for all observed behavior consistently.